I'm sure this has been discussed before (I searched for "drag" and "drop" but nearly everything that came up was related to FTP Batch uploads). It would be very convenient to be able to reorder photos by simply dragging them. I have so many photos in some albums that using the traditional method requires me to know all the photos by filename, and that can get very tedious after a while. Just a suggestion.
Other than that, I'm loving Coppermine and don't think I'll ever switch.
Has already been done for cpg1.5.x.